Function TransferAlways

cpp/src/arrow/util/thread_pool.h:134–136

  // This can be useful in cases where you want to ensure parallelism
  template <typename T>
  Future<T> TransferAlways(Future<T> future) {
    return DoTransfer(std::move(future), true);
  }

  // Submit a callable and arguments for execution.  Return a future that
  // will return the callable's result value once.